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Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Fixed income securities, amortized cost	$ 3,451,149	$ 5,271,818
Other Investments	$ 391,217	$ 431,630
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	20,000,000	20,000,000
Preferred stock, shares issued	0	0
Preferred Stock, Shares Outstanding	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	130,000,000	130,000,000
Common Stock, Shares, Outstanding	45,336,278
Fixed Income Securities [Member]
Fixed income securities, amortized cost	$ 3,020,744	$ 4,614,623
Equity investments in pooled funds [Member]
Other Investments	351,049	366,939
Other Investment Not Readily Marketable, Fair Value	351,049	396,689
Collateral Pledged [Member] | Fixed Income Securities [Member]
Fixed income securities, amortized cost	0	99,719
Parent Company [Member]
Fixed income securities, amortized cost	151,007	239,476
Other Investments	$ 40,168	$ 64,691
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	20,000,000	20,000,000
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	130,000,000	130,000,000
Common stock, shares issued	45,365,170	45,275,982
Common Stock, Shares, Outstanding	45,365,170	45,275,982
Treasury stock, shares	28,892	24,816
Short-term Investments [Member]
Fixed income securities, amortized cost	$ 430,405	$ 557,476
Short-term Investments [Member] | Parent Company [Member]
Fixed income securities, amortized cost	$ 192,996	$ 69,531

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